Coordination and protection of busbar distribution

Transcription

1 Technical collection Coordination and protection of busbar distribution Low voltage expert guides n 1

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3 Content Busbar distribution system Performance criteria of a LV Busbar distribution Functions 6 Level A: transmission and distribution with a small quantity of tap points 6 Level B: distribution with a large quantity of tap points 6 Level C : the final distribution IEC standard BBT protection 9 Overload protection 9 Short-circuit protection by circuit breaker 1 Circuit breaker/busbar trunking coordination Busbar distribution coordination Summarizing busbar distribution characteristics 4 The Schneider Electic busbar distribution System BBT/circuit breaker coordination 8 Protection of a transmission or distribution BBT downstream from the Main Switchboard (MSB) 8 Protection of an BBT by an NSX400N limiting circuit breaker Exclusive features of the Schneider Electric system: enhanced busbar distribution coordination Final distribution Advantages of the Schneider Electric system 22 BBT protection 22 Tap off boxes 22 Final distribution Advantages and exclusive features of the Schneider Electric system 23 Comprehensive coordination choice guide tables 23 Standard performance circuit breakers for all Isc y 70 ka 23 Optimization of the tap off box offer 23 Summarizing table 24

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5 Busbar distribution Design and production of a busbar distribution installation for industrial and commercial buildings must meet 3 main requirements: progressive upgradeability of the installation, simplicity and dependability. Busbar distribution ensures these requirements are fully met Performance criteria of a LV Busbar distribution Three performance criteria for a busbar distribution installation: b b b upgradeability simplicity dependability 1. Progressive upgradeability of the installation Flexibility and Adaptability have become the key words in all commercial and industrial activities which need to quickly adapt to the market in order to: b meet their customers needs, b cope with rapid changes and fluctuations in demand. These performance criteria are expressed in terms of: b quantity of goods to be produced or of services to be provided... b continually decreasing manufacturing lead time, b quality: the level of quality of the products and associated services must be equivalent whatever the decisive parameters (short lead time, large quantity to be produced,...). This implies permanent adaptation of production means as production rates are stepped up after initial commissioning, and the process is completed by new machines. Busbar distribution, with its highly flexible design, fully covers these requirements. 2. Simplicity of the busbar distribution b Easy to design: the study is feasible regardless of energy distribution and load layout. Choice of equipment is predetermined and optimized. b Easy to install thanks to the factory-built concept. 3. Dependability Dependable electrical distribution is optimized as a means of guaranteeing: b safety of persons and equipment b continuity of service (choice of grounding system, implementation of discrimination techniques, breaking not required when making changes to the installation...) b reliability (reliable switchgear, factory-mounted subassemblies...) b easy maintenance (simple, rapid modifications). Dependability also guarantees an economic operating solution. Busbar distribution fully meets these criteria. 3

6 Busbar distribution Distribution is divided up into 3 separate levels between the transformer and the final applications: b level A: Transmission and distribution with a small quantity of tap points, b level B: Distribution with a large quantity of tap points b level C: the final distribution. Busbar Trunking (BBT) distribution fully covers the requirements of each level by providing: b functions that are often specific in nature; b a high degree of operating reliability in compliance with the IEC standard. In large sites Buildings in excess of m² The following diagrams represent standard installations which cover most cases encountered in practice. DB TØ transmission MSB T1 transmission with a small quantity of tap points workwhop 1 supply 1000 to 5000 A hall 2 supply Isc 30 to 80 ka hall 3 supply workshop 2 supply hall 1 supply Isc 20 to 50 ka distribution with a large y 400 A quantity of tap points bay 1 supply bay 2 supply i 800 A Isc 20 to 70 ka 100 to 250 A Isc 10 to 40 ka automation enclosure y 40 A y 5 to 10 ka socket enclosure y 40/ 63 A y 10 to 16 ka Isc 10 to 15 ka lighting y 25 A (40 A) automation enclosure y 400 A y 160 A 15 to 25 ka y 400 A 20 to 70 ka M NB. right next to the machine or built into the machine use M M manufacturing process moving tool (maintenance, servicing) lighting large manufacturing process industry 4

7 Busbar distribution In medium-sized and small sites Buildings smaller than m² DB Level A Transmission and distribution with a small quantity of tap points. Note : does not concern medium-sized and small sites. 400 A 15 ka 10 to 15 ka Level B Distribution with a large quantity of tap points. 100 to 250 A warehouse storage y 5 ka < 63 A 10 to 15 ka Level C Energy utilisation. ID63 s 60 A 25 to 40 A 10 ka 30 ma PC homogeneous load, offices M final distribution purpose of building lighting 5

8 Busbar distribution 1.2. Functions BBT in transmission and distribution with a small quantity of tap points b High current ratings from 1000 A to 5000 A b High short-circuit withstand up to 150 ka b Technological continuity b Flexibility BBT in Distribution with a large quantity of tap points: b numerous tap off sockets b box positioning flexibility b safe, easy handling Final distribution: b on-load opening (emergency breaking) b local disconnection. Level A: transmission and distribution with a small quantity of tap points Requirements This level corresponds to Transformer/Main Switchboard (MSB) supply and main distribution downstream from the Main Switchboard (MSB). The requirements of this level as far as performance criteria are concerned (see p. 3) are summarized in the table below: Performance criteria Requirement Comments Upgradeability b b modifications at this level of the installation although rare are important; new layouts do not affect main distribution Simplicity b b b Power is available at all points of the installation as from the design stage. Implementation simplified by the factory-built BBT concept. Dependability b continuity of service b b b Distribution is entirely placed downstream. Maintenance is performed with power on. b safety b b Safety of persons must be guaranteed. Maintenance is rare and is carried out by qualified staff. A high degree of reliability in the event of an electrical fault is required. b minor requirement b b average requirement b b b major requirement Busbar Trunking (BBT) with a small quantity of tap points for transmission and distribution The T0 busbar trunkings convey energy from the MV/LV transformer directly to the Main Switchboard (MSB). The T1 busbar trunkings, downstream from the Main Switchboard (MSB), convey and distribute energy to BBTs with a large quantity of tap points which supply the various workshops. Use transmission and distribution BBTs with a small quantity of tap points ensures a simple, suitable solution: b the characteristics of the transmission BBTs authorize current ratings ranging from 1000 A to 5000 A and short-circuit withstand levels up to 150 ka. b use of a flexible link to level B BBTs ensures technological continuity and flexibility of the installation. b BBTs have a small quantity of tap points, as the number of feeders to be supplied (workshops, halls) is small. b tap off boxes are of the power on fixed or withdrawable type. Level B: distribution with a large quantity of tap points Requirements Two types of loads must be supplied downstream from the distribution BBTs: b workshops and large machines (automation cubicle). In this case the short-circuit and current levels may still be high (20 to 70 ka respectively and up to 800 A) (see large sites on page 4). b bays and small machines (switchboard, automation enclosure, lighting circuit...). Short-circuit and power levels are lower, 10 to 40 ka respectively and up to 400 A. 6

9 Busbar distribution Performance criteria are summarized in the table below. Performance criteria Requirement Comments Upgradeability b b b Major modifications are possible. The tap off points (loads) evolve physically and electrically, thus calling for: distribution with high density tap off sockets, upgradeability without interrruption of service continuity. Simplicity b b b On design and installation. It must be possible to place the tap off boxes anywhere on the busbar trunking whatever the Isc level. Dependability b continuity of service b b b Modifications are made without breaking. The tap off boxes can be connected and disconnected with power on. b safety b b b Modifications made with power on must be 100% safe: direct contact protection polarization for proper installation of the tap off boxes performances of the tap off box equipped with its circuit breaker automatically compatible with the Isc at the considered point. b minor requirement b b average requirement b b b major requirement Busbar Trunking (BBT) with a large quantity of tap points for distribution BBT distribution meets the operator s needs: b a large quantity of tap off sockets b 100% safe connection of tap off boxes with power on b boxes can be placed anywhere on the BBT b easy, fully safe disassembling/reassembling/addition of tap off boxes b protection device placed near to the user, thereby ensuring easy handling. Busbar Trunkings comply with the IEC standard (see page 9) which guarantees their quality and reliability whatever changes are made to the installation. Level C : the final distribution Requirements Downstream final distribution is often linked to the load. The performance criteria requirements are: Performance criteria Requirement Comments Upgradeability b b b The BBT tap off boxes must be Simplicity b b standard. Protection devices must have a wide setting range. Dependability b continuity of service b b b It is vital that protection of the load(s) in the automation cubicle be fully coordinated with the upstream protection devices. b safety b b b Of persons and equipment. b minor requirement b b average requirement b b b major requirement 7

10 Busbar distribution The final distribution It must meet a number of characteristics in order to ensure system performance, in particular as concerns continuity of service and safety. On-load opening, necessary for emergency breaking, and disconnection are requirements to be built into the enclosure incoming switch. Moreover, the control and protection switchgear are easily accessible to the user, thus making them easy to handle. DB BBT DB BBT tap off circuit breaker tap off circuit breaker connecting cable connecting cable automation cubicle isolating switch final distribution enclosure isolating switch industrial control circuit breaker final distribution circuit breaker 1.3. IEC standard IEC LV switchgear assemblies IEC Second part : specific busbar trunking rules. General Area of application: busbar trunkings for power and lighting distribution. Factory quality Manufacturer s guarantee characterizing the product. Product quality and dependability guaranteed by a series of factory tests. This standard concerns LV switchgear assemblies. Busbar trunkings must comply with the rules laid down in publications and 2. Définitions Busbar trunking: Switchgear type tested assembly in the form of a conductive network concerning, in a duct, cableway or similar enclosure, busbars which are supported by insulating materials. This assembly can be made up of: b b b busbar parts with or without tap off points, power supply, flexible links, branch busbar parts. Electrical characteritics of the assemblies The manufacturer must specify the mean values for the various phases: R: mean ohmic resistance of the busbar trunking per meter X: mean reactance of the busbar trunking per meter Zf: impedance per meter of loop length, including the protection circuit (PE) and the phase giving the highest impedance. Indirect contact protection by automatic power supply breaking using over current protection devices. 8

11 Busbar distribution Construction arrangements Busbar trunkings must be designed as type tested LV switchgear assemblies (TTA). According to the manufacturer s instructions, BBTs are designed to withstand mechanical loads. For safety reasons, an BBT equipped with tap off points must be designed in such a way as to prevent incorrect connection of the tap off parts. If three-phase ac is used, phase order must be constant throughout the BBT. Temperature rise limits are defined on the enclosures and connection terminals. Test specifications Type tests are designed to check compliance with the specifications laid down for a given BBT type. Type tests are carried out on a copy of an BBT or on an BBT type produced using the same or similar drawings. Type tests consist of: b checking temperature rise limits, dielectric properties, short-circuit withstand, electrical continuity of the protection circuit, clearances and creepage distances, mechanical operation, degree of protection, resistance, reactance and impedance, and sturdiness of the construction. The standard describes all the conditions and provisions of the tests laid down and, if necessary, the results to be obtained BBT protection A 20% shift of the opening currents results in a minimum overcalibration of 10% of the busbar trunking if fuse protection is used. This must be provided in accordance with installation standards. Overload protection DB t(s) 1.25 to 1.6 In The busbar trunking supplies loads: the total load current is lr. Sizing characteristics for choice of BBT and overload protection are: b current rating lb = k1 x IT (k1 is the concentrationfactor) b rated busbar trunking current lnc > lb b permissible current as a function of temperature lz = f1 x lnc (f1 is the temperature factor) b derating factor k2 linked to the type of switchgear: v fuse k2 = 1.1 v circuit breaker k2 = 1 DB Fuse. t(s) 1000 In Iz = 1.1 In 1.45 Iz Iz = Inc if fz = to 1.3 In I For extension purposes, busbar trunking is normally protected for its rated current lnc (or for their permissible current lz if the temperature factor f1 is applied). In order to take account of busbar trunking thermal overload protection, the various protection switchgear technologies and the maximum opening currents for protection devices in overload conditions must be considered. b Calibration of thermal asymptotes: v the distribution fuse is calibrated to trip on overloads of between 1.25 and 1.6 times its rated curent (fuse ln) v the circuit breaker is calibrated to trip on overloads of between 1.05 and 1.3 (1.2 for circuit breakers with electronic protection) times its setting current (lr as a function of circuit breaker ln) b Maximum opening current: v this current is set at most by the installation standards (IEC 60364, NFC ,...) to 1.45 times the current permissible to the busbar trunking. In Iz = In 1.45 Iz Circuit breaker. I 9

12 Busbar distribution Example for a current lb = 400 A in an ambient temperature of 35 C: v fuse protection: lnc = lb x f1 x k2 = 400 x 1 x 1.1 = 440 A The busbar trunking chosen is KSA50 (lnc = 500 A) v circuit breaker protection: lnc = lb x f1 x k2 = 400 x 1 x 1 = 440 A The busbar trunking chosen is KSA40 (lnc = 400 A) If operating conditions are different from rated conditions of use, the circuit breaker offers enhanced optimization of busbar trunking protection (e.g. operation at high ambient temperatures of 45 /50 C). Setting circuit breakers equipped with electronic trip units: b thermal protection lr adjustable from 0.4 ln to ln b short-circuit protection from 2 lr to 10 lr b increased flexibility and upgradeability. Fineness of the thermal setting b The fuse is given a fixed rating. Current changes in the device to be protected require fuse replacement. The difference between 2 fuse ratings is approximately 25 %. Standard ratings are given according to the series of characteristic numbers of the Renard series. For example: etc. b The circuit breaker offers a setting fineness of: v 5 % for circuit breakers equipped with conventional thermal-magnetic trip units, v 3 % for circuit breakers equipped with electronic trip units. For example: a circuit breaker with a nominal rating of 100 A can easily be set to values of lr = 100 A, 95 A, 90 A, 85 A, 80 A. For example: a circuit breaker with a nominal rating of 100 A set at 90 A will be used to protect a KSA10 busbar trunking (lnc = 100 A) which is used for an ambient temperature of 50 C (see table of maximum permissible temperatures as a function of operating temperature). Extensive setting range of circuit breakers equipped with electronic trip units Circuit breakers equipped with electronic trip units or setting dynamics in: b thermal protection lr adjustable from 0.4 ln to ln b short-circuit protection from 2 lr to 10 lr For example: a 250 A circuit breaker (NSX250N equipped with a Micrologic 2.2) can easily be set in: b thermal protection of 100 to 250 A b short-circuit protection of 200 to 2500 A DB Exemple of setting possibilities. This ensures a high degree of flexibility with respect to: b modifications (flexibility), extensions (upgradeability): protection devices are easily adapted to the application requiring protection and to the grounding system used (protection of persons and equipment) b maintenance: use of this type of device considerably reduces maintenance component stocks. 10

13 Busbar distribution BBT sizing is determined by 3 types of characteristics: b the maximum peak current, peak l b the maximum short-term rms current, lcw b the thermal stress (in A 2 s). Short-circuit protection by circuit breaker Inherent BBT characteristiques BBT short-circuit sizing is determined by the following characteristics: the maximum peak current, peak l: this characteristic expresses the instantaneous electrodynamic withstand limits of the busbar trunking. Peak current value is often the most restrictive instantaneous characteristic for the protection device. maximum short-term rms current lcw: this characteristic expresses the permissible temperature rise limit of conductors for a given period of time (0.1 to 1 s). the thermal stress in A 2 s: this characteristic expresses the instantaneous thermal stress withstand of the BBT. Normally, if the short-circuit generates fault conditions that are compatible with the first two characteristics, this constraint is naturally satisfied. The assumed short-circuit current to be considered for BBT protection is the one found at supply box level. Circuit breaker characteristics Circuit breaker D must meet the requirements of product construction standards (IEC ,...) and installation standards (IEC or relevant country standards), i.e. its breaking capacity lcu (1) must be greater than short-circuit current Isc at the point where it is installed. (1) installation standard IEC 364 and the construction standards specify that the breaking capacity of a circuit breaker is: the ultimate breaking capacity, lcu, if it is not coordinated with an upstream protection device the breaking capacity enhanced by cascading, if there is coordination with the upstream protection device. Applications Two cases must be considered : v directely protected busbar trunking circuit breaker lcu u assumed Isc at point A BBT peak l u asymmetrical assumed or limited Isc at point A BBT thermal withstand in lcw u thermal stress passing through the BBT v busbar trunking protected downstream from a cable circuit breaker lcu u assumed Isc at point A BBT peak l u asymmetrical assumed or limited Isc at point B BBT thermal withstand in lcw u thermal stress passing through the BBT. Circuit breaker/busbar trunking coordination DB I1 busbar trunking busbar trunking peak I Icw (u T) T = 1s asymm Isc Isc T Current value of the 1 st peak as a functon of rms Isc. This coordination depends on the type of circuit breaker protecting the busbar trunking. Non-limiting or time-delayed circuit breaker These are non-limiting (instantaneous or time-delayed) circuit breakers and timedelayed limiting circuit breakers, mainly of the air power (> 800 A) type. The busbar trunking must be able to withstand the fault peak current to which it may be submitted as well as thermal withstand during any time delay: b the permissible peak current, peak l, of the BBT must be greater than the peak value of the assumed asymmetrical short-circuit current, asymm. Isc, at point A. The value of the asymmetrical short-circuit current is obtained from the value of the symmetrical short-circuit current, Isc, multiplied by a standardized asymmetry factor (k). The first value of the 1st short-circuit asymmetry peak in the transient state is the one that is taken into account. 11

14 Busbar distribution DB Ipeak (ka) ka rms Isc 0 4, Transcient and steady states of a short-term short-circuit. Standardized table for calculating the asymmetrical short-circuit Isc: assumed symmetrical short-circuit ka (rms value) 4.5 y I y < I y < I y < I y < I 2.2 Assymetric factor k For example: for a circuit with a assumed short-circuit current of 50 ka rms, the first peak reaches 105 ka (50 ka x 2.1): see figure opposite. b The short-term short-circuit current, lcw, of the BBT, must be greater than the current flowing through the installation for the duration of the short-circuit Isc (duration T - total breaking time - including the time delay if any -). For example: a KTA16 BBT has an lcw characteristic of 60 ka for T = 1 second, i.e. a thermal stress withstand expressed in A 2 s equal to 3.6x109 A 2 s. If one of these relationships is not verified, a suitable higher rating must be chosen for the BBT. DB Limiting circuit breaker This mainly concerns protection of BBTs by moulded case type circuit-breakers (u 1250 A). In this case it is ensured that the BBT withstands the peak current limited by the protection device and the corresponding thermal stress. b The current limited (peak l) by the circuit-breaker is y the peak current permissible to the BBT. b The thermal stress limited by the circuit-breaker is y the thermal stress permissible to the BBT. Cheking BBT withstand in peak I non-limiting peak current I peak (ka) I sc I peak maximum current permissible to the busbar trunking peak current limited in the busbar trunking I L current limitation curve assumed short-circuit current Icc DB Checking BBT withstand in A 2 S thermal stress permissible to the busbar A 2 s thermal stress limited in the busbar trunking thermal stress limitation curve assumed short-circuit current Icc If either of these conditions is not met, oversizing of the BBT will be required. 12

15 A' A Busbar distribution Time-delayed non-limiting circuit breaker Limiting circuit breaker BBT protection summarizing table Network characteristics Isc Circuit breaker characteristics / Short-circuit constraints Icu u Isc at point A BBT characteristics / Short-circuit constraints (1) Peak I Icw for T (3) A 2 s BBT withstand Permissible Instantaneous at peak current short-term current thermal withstand kâ ka rms x f(t) ka 2 s Peak I u Isc x k (2) Peak I u I L limited by the circuit breaker Icw u Isc ka 2 s (BBT) u ka 2 s limited by the circuit breaker Characteristics that are not applicable or that are naturally verified (1) the Isc of the network under consideration is that at the BBT connection point (at point A) (2) asymmetry factor (see page 13) (3) T: total breaking time including any time delays. DB DB circuit breaker Isc at point A circuit breaker cab le BBT B BBT b The busbar trunking short-circuit protection level can be either total or partial: v total protection: the busbar trunking is protected up to the ultimate breaking capacity of the circuit breaker v partial protection: the busbar trunking is protected up to a high short-circuit current level (e.g. 55 ka) but less than circuit breaker ultimate breaking capacity (lcu) (e.g. lcu = 70 ka). DB I peak (Â) BBT 1 partial protection total protection DB I peak (Â) BBT 1 partial protection total protection BBT 2 BBT 2 circuit breaker curve limiting circuit breaker curve I (12 ka) Icu (25 ka) BBT2 protection limit Isc I (25 ka) BBT2 protection limit Icu Isc (150 ka) Non-limiting circuit breaker. Limiting circuit breaker. 13

16 Busbar distribution 1.5. Busbar distribution coordination Protection device coordination: System performance is guaranteed by standardization of circuit breaker protection and BBT busbar distribution. The performance of a busbar distribution system depends on the specific characteristics of each of its component parts. This performance will be optimized by providing proper coordination, obtained by a system type design. Continuity ofservice and discrimination The previous chapters dealt with BBT overload and short-circuit protection. An installation is always made up of a number of distribution levels. Continuity of service must be guaranteed by ascending coordination of protection devices from the load to the source. This coordination relies on discrimination techniques. Discrimination of protection devices consists of coordinating automatic protection devices so that a fault occurring at any point of the network is eliminated by the circuit breaker immediately upstream from it and by this circuit breaker alone. The performance of an electrical distribution system is guaranteed by standardization of circuit breaker protection and BBT busbar distribution Summarizing busbar distribution characteristics The performance criteria of a distributed electrical distribution installation in industrial and commercial buildings call for functions whose characteristics are summarized in the table below. Criteria Relevant functions Level A transmission and distribution with a small quantity of tap points Level B distribution with a large quantity of tap points Level C final distribution Upgradeability numerous tap off points v b Simplicity easy study and installation b b v easy site modification v b v Continuity of service discrimination of protection devices b b b modification with power on v b protection device easily reset v v b Safety controlled fault parameters (1) b b b on-load braeking and disconnection b b b b vital maximum performance v normal performance (1) System global control - Circuit breaker protection device coordination - Inherent BBT performance - Protection of persons and equipment - Compliance with standards - etc... 14

17 The Schneider Electic busbar distribution System Busbar distribution fully satisfies requirements for upgradeability, simplicity, continuity of service and safety. Schneider Electric recommends a System type approach to perform the above functions. These solutions are based on a BBT busbar distribution system, protected by circuit breakers, and provide: b b b simplicity of choice homogeneity of solutions rationalization of components a manufacturer s guarantee of System coordination. b The two block diagrams on the following pages give some examples of the Schneider Electric circuit breaker protected busbar distribution system. 15

18 N push to trip push to trip push to trip push to trip N The Schneider Electic busbar distribution System In large sites Buildings in excess of m² DB DB KTA20 Level A KSA40 KTA20 KSA16 Level B KBB Level C Example of an industrial site. 16

19 OFF T push to trip push to trip The Schneider Electic busbar distribution System In medium-sized and small sites Building smaller than m² DB DB KSA16 Level B KNA63 KBA Level C Example:of a supermarket. 17

20 The Schneider Electic busbar distribution System 2.1. BBT/circuit breaker coordination In order to simplify choice, Schneider Electric presents the results of each circuit breaker/ BBT combination directly in table form (see Technical complementary data). The approach used in the study examined earlier, applied to Schneider Electric products, enhances the Schneider Electric system. Protection of a transmission or distribution BBT downstream from the Main Switchboard (MSB) The diagram opposite shows a T1 transmission BBT and a KTA16 distribution BBT (1600 A) protected by a Masterpact M16 circuit-breaker with a 0.5 s time delay. b At point A, at the supply end of the KTA16 distribution BBT, the Isc is 55 ka. The conditions laid down on page 15 are carefully verified: b for the Masterpact Isc (65 ka) > Isc (55 kw) at point A of the installation b for the busbar trunking: v the withstand current lcw (66 ka) for 1 s is greater than the short-circuit current Isc (55 ka) for T = 0.5 s v the peak withstand, peak l (130 kâ) of the busbar trunking is greater than the maximum asymmetrical peak current. The following table lists the various constraints and characteristics of the circuit breaker and busbar trunking. Network characteristics at point A Isc = 55 ka in A Circuit breaker characteristics / short-circuit constraints Icu = 65 ka u 55 ka in A BTT characteristics / short-circuit constraints Peak I = 130 ka Icw = 66 ka for 1s A 2 s BBT withstand Permissible short-term Instantaneous at peak current current thermal withstand kâ ka rms x f(t) ka 2 s Non-limiting circuit breaker 130 ka u 55 ka x 2,2 66 ka u 55 ka fot 1s Naturally verified characteristics. DB DB Protection of an BBT by an NSX400N limiting circuit breaker Limiting capacity The circuit breakers in the Compact NSX range are limiting circuit breakers with a high limiting capacity. A circuit breaker s limiting capacity expresses its ability only to let a limited current I L lower than the assumed Isc asymmetrical peak short-circuit current, through on a short-circuit. The consequence is a considerable reduction in electrodynamic and thermal stresses in the installation requiring protection. 18

21 The Schneider Electic busbar distribution System DB assumed Isc at "A" 45 ka NSX400N Applying limiting capacity to BBT protection This fault current limitation means that BBT protection level is extremely high. With Compact NSX circuit breakers, a 10% limitation (I L /asymmetrical Isc) reduces to less than 1% the fault current flowing through the installation. The diagram opposite shows protection of the KSA40 distribution busbar trunking by an NSX400N limiting circuit breaker. In this diagram: b the Isc is 45 ka at point A. A study of the various limitation curves shows that: b in B, the limited Isc is only 26 ka (instead of nearly 84 ka without limitation) b the energy limited in A 2 s is far lower than BBT withstand. DB ka peak assumed Isc KSA40 at "B" 40 ka Protection of an BBT by an NSX400N limiting circuit breaker. 48 kâ 26 kâ a. current limitation 40 ka Isc DB A 2 s 354 x x ka Isc b. energy limitation The following table lists the various constraints and characteristics of the circuit breaker and BBT. Network characteristics Isc = 45 ka at point A Isc = 40 ka at point B Circuit breaker characteristics / Short-circuit constraints Icu = 45 ka u 45 ka at point A BBT characteristics / Short-circuit constraints (at point B) Peak I = 48 ka Icw = 66 ka for Ts "A 2 s" = 354 x 106 A 2 s BBT withstand Permissible short-term Instantaneous at peak current current thermical withstand kâ ka rms x f(t) ka 2 s Limiting circuit breaker 48 kâ u I L = 28 kâ 354 x 106 u 1,6 x 106 A 2 s Unapplicable characteristics. This table shows that the limitation performance of the Compact NSX is vital to reduce the stresses to which the busbar trunkings are subjected and in particular the thermal stress. 19

22 The Schneider Electic busbar distribution System The exceptional limitation of the peak current means that monitoring of the BBT thermal stress criterion can be ignored (limited I 2 t << BBT withstand I 2 t). The following limitation curves immediately show the coordination characteristics. DB DB x A 2 s KSA63 (630 A) 13.6 Ipeak kâ KSA63 KSA40 KSA16 KSA10 KSA25 Limited î and Canalis. N H NSX630 NSX400 NSX250 NSX160 NSX100 L Isc KSA40 (400 A) KSA25 (250 A) KSA16 (160 A) KSA10 (100 A) Limited A 2 s and Canalis. N N N H H H L L NSX630 NSX400 NSX250 NSX160 L NSX100 Isc These diagrams show that protection is provided in excess of the maximum Isc encountered on installations Exclusive features of the Schneider Electric system: enhanced busbar distribution coordination Enhanced coordination has many advantages: exclusive features of the Schneider Electric system b possibility of installing circuit breakers with standard breaking capacity (anywhere on the tap off BBT) downstream from an BBT protected by a Compact NSX. b standard guarantee of total distribution discrimination. This results in reduced installation and operating costs. DB Coordination between a Compact NSX circuit breaker (D1 placed upstream) and a downstream circuit breaker (D2) protecting an BBT, enhances the Isc withstand performance of this BBT. Enhancement depends on the limitation performances and breaking technique of the Schneider Electric circuit breakers. Reminder: coordination between 2 protection devices When 2 circuit breakers are installed in series in an electrical installation, their behavior when a short-circuit occurs downstream is referred to by the term coordination (see diagram opposite). This term covers 2 notions: b discrimination: only the circuit breaker placed immediately upstream from the fault eliminates the fault b cascading: the upstream circuit breaker uses its limiting capacity to help the downstream circuit breaker eliminate the fault on breaking. Thus, according to the level of short-circuit to be eliminated, D1 and D2 may be: b discriminating: only D2 will eliminate downstream faults b cascading: D1 will help D2 eliminate short-circuits. In this case D2 s short-circuit capacity will be enhanced. Coordination. Implementation of a D1 upstream Compact NSX circuit breaker of the Compact NSX type coordinated with a D2 downstream circuit breaker, simultaneously enhances: b breaking capacity by cascading of circuit breaker D2, b as well as the discrimination level up to the enhanced breaking capacity of the combination. Coordination is defined and recognised by the switchgear standards (IEC 60947) and installation standards (IEC or relevant country standards), and is guaranteed by manufacturing tests or calculations. 20

23 The Schneider Electic busbar distribution System DB Application: enhanced BBT protection This cascading technique also considerably enhances BBT withstand characteristics with respect to the assumed short-circuit current. In the diagram opposite the KSA40 busbar trunking is protected by the NSX400N circuit breaker (D1). A KSA16 tap off protected by an NSX160F (D2) circuit breaker is placed on this busbar trunking. b Without coordination, the very high limiting capacity of the NSX160F alone already protects the KSA16 up to its ultimate breaking capacity Icu, i.e. 35 ka. b However coordination performance is enhanced as a result of enhanced coordination with the upstream NSX400N: v enhanced breaking capacity of the NSX160F which rises to 45 ka, v enhanced discrimination: due to the techniques developed in the NSX type ranges, discrimination is total between the 2 protection devices, in other words up to the enhanced breaking capacity of D2, i.e. 45 ka. v enhanced busbar trunking withstand: tested coordination of Canalis KSA16 is enhanced up to the enhanced Isc of the NSX160F, i.e. 45 ka. This exclusive Schneider Electric system feature increases: b reliability, thanks to the high limitation of short-circuit current thermal and electrodynamic stresses b continuity of electrical distribution service thanks to the increased discrimination level. Enhanced protection of a KSA-16 BBT by an NSX160F circuit breaker coordinated with an NSX400N circuit breaker. Canalis KSA 16 BBT protection Protected by limiting D2 NSX160F Icu = 35 ka BBT protection in coordination Protection limit KSA16 Isc = 35 ka Isc = 45 ka Protected by limiting D2 NSX160F Icu = 35 ka coordinated upstream with D1 NSX400N Icu = 45 ka Descrimination limit Up to max. Isc = 35 ka according to upstream Up to max. Isc = 45 ka guaranteed KSA16 characteristic Maximum stresses on BBT if a short-circuit occurs Peak I = 22 kâ A 2 s = 20,2 106 Isc = 35 ka I L = 19 kâ A 2 s = 0, Isc = 45 ka I L = 20 kâ A 2 s = 0, Final distribution The following diagrams optimize all the functions required for all industrial and commercial building applications. Protection b switchboard overcurrent protection is provided by the protection circuit breaker (DD) installed in the tap off box. b feeder protection is provided by the circuit-breakers (DCI) installed at each feeder. Continuity of service is optimum at feeder level: b thanks to enhanced total discrimination between the protection devices b thanks to easy access and resetting of the protection devices. Maintenance The switchboard incoming switch (IS) guarantees disconnection and thus safety for maintenance, servicing and upgrading of the installation. 21

24 The Schneider Electic busbar distribution System On-load opening This function is performed by a switch. The incoming switch places the installation out of operation should a problem arise, either by manual control or automatically using an emergency punch button. This safety function requires a high degree of reliability should a fault occur on the electrical installation. DB Canalis DB Canalis tap off circuit breaker DD tap off circuit breaker connecting cable connecting cable automation cubicle final distribution enclosure isolating switch IS isolating switch Industrial control circuit breaker DCI final distribution circuit breaker 2.4. Advantages of the Schneider Electric system DB Canalis KSA busbar trunking. BBT protection Schneider Electric circuit breakers offer: b overload and short-circuit protection, b an extensive setting range and thus protection device standardization, b coordination between the protection devices and the Telemecanique Canalis BBTs: v total discrimination: 1 to 6300 A between all Merlin Gerin circuit breakers v cascading: - enhancement of low and medium power BBT short-circuit protection devices, thus meeting all the short-circuit levels encountered. - tap off protection using standard circuit breakers regardless of where the tap off box is placed on the Canalis BBT. b use of standard circuit breakers simplifies the study process, while ensuring a high degree of dependability. b quick, easy fault tracking. b simple reclosing ( resetting ) once the fault has been eliminated by the operator. DB Tap off box. Tap off boxes The Schneider Electric Canalis tap off boxes satisfy operators needs in terms of: b installation upgradeability without production downtimes b continuity of service b safety. The tap off boxes: b b can be connected and disconnected with power on without risk to the operator are designed for installation at one-meter intervals on the distribution BBTs. 22

25 The Schneider Electic busbar distribution System DB Prisma enclosure. DB Final distribution The protection switchgear optimizes switchboard functions. b Coordination of upstream protection devices is provided and guaranteed by Schneider Electric: v for distribution applications between Masterpact, Compact C, Compact NSX circuit breakers and Multi 9 circuit breakers. v for industrial control applications between circuit breakers and control (motor circuit breaker, Integral,...). The coordination tables are available in the relevant product catalogs. The Schneider Electric switches comply with the IEC standard, and are designed to ensure AC23 on-load breaking and disconnection. Their protection is guaranteed by coordination with the upstream circuit breakers. Automation enclosure. DB Switch Advantages and exclusive features of the Schneider Electric system Total coordination of the Schneider Electric system guarantees and enhances safety of persons and equipment, continuity of service and installation upgradeability and simplicity. Total coordination is materialized by: Comprehensive coordination choice guide tables b Schneider Electric proposes coordination tables for a busbar distribution system from 1 to 5000 A: v circuit breakers: Multi 9, Compact NSX, Compact CM, Masterpact v from 1 to 6300 A. v BBT: lighting BBT, low, medium and high power distribution BBT. b Whatever the installation s short-circuit current, 2 table types directly supply the appropriate BBTs and circuit breakers: v v one to ensure coordination the other to ensure cascading and enhanced discrimination. Standard performance circuit breakers for all Isc y 70 ka The BBT tap off boxes are equipped with standard Compact NS circuit breakers and can be installed at any point of the BBT. Optimization of the tap off box offer The extensive setting ranges of the circuit breakers equipped with electronic trip units. b in thermal protection, Ir is adjustable from 0.4 to In, b in short-circuit protection, Im is adjustable from 2 to 10 Ir, allow optimization of the tap off box stocks required for maintenance and extension purposes. This feature helps enhance the natural flexibility and upgradeability of the BBTs. 23

26 The Schneider Electic busbar distribution System Summarizing table Criteria Relevant functions Level A Transmission and distribution with a small quantity of tap points Upgradeability One tap off connection every meter BBT Level B Distribution with a large quantity of tap points Level C Final distribution Extensive setting range of protection devices CB CB Easy installation BBT BBT Standard performance circuit breakers for all Isc y 70 ka CB CB Simplicity Comprehensive coordination choice guide tablr BBT, CB BBT, CB BBT, CB Optimization of the tap off box offer CB CB Easy, rapid BBT installation BBT BBT Easy installation modification BBT BBT Extensive protection enclosure range BBT BBT Continuty of service Total discrimination of BBT protection devices BBT, CB BBT, CB Total discrimination of protection devices for all Merlin Gerin and Telemecanique circuit breaker ranges (1) CB Modification without production downtimes BBT BBT Safety of persons and equipment Easily resettable protection device CB CB CB System coordinated from 40 to 5000 A cascading and total coordination of protection devices BBT, CB BBT, CB BBT, CB On load breaking and disconnected coordinated with upstream protection devices CB CB CB Testable protection devices CB CB CB Polarized tap off boxes BBT BBT : exclusive advantage of the Schneider Electric system. BBT : performance owed to the Canalis BBTs CB : perfromance due to the circuit breakers BBT, CB : performance due to the coordination between BBTs and circuit breaker (1) In particular thanks to : a system coordinated from 40 to 5000 A cascading and total coordinition of protection device. 24

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28 Schneider Electric Industries SAS 35, rue Joseph Monier CS F Rueil Malmaison Cedex RCS Nanterre Capital social As standards, specifications and designs change from time to time, please ask for confirmation of the information given in this publication. This document has been printed on ecological paper Design: Schneider Electric Photos: Schneider Electric Printed: Schneider Electric - All rights reserved. DBTP118EN